Experimental Investigation on the Structural Behavior of Composite Concrete Bridge Girders with Tall Haunches

This paper outlines the results of an investigation on the structural behavior of tall concrete haunches in prestressed concrete (PSC) bridge girders and considers the behavior of girders with both cast-in-place concrete and partial-depth precast concrete panel deck slabs. The haunch is generally a region of cast-in-place concrete between the top of a girder and the bottom of the bridge deck. The haunch serves an important purpose of maintaining a uniform deck thickness while accounting for differential camber between adjacent girders and other necessary adjustments during construction. In some cases, the haunch is used to account for bridge cross-slope; however, in many cases, it is used to address unpredictable issues during construction. Although most designs typically limit the range of haunch heights to 0–90 mm (0–3.5 in.) without special detailing, deeper haunches of 300 mm (12 in.) or more may sometimes be required due to geometric requirements or to address construction problems. In many instances, decisions on increased haunch depths and detailing must be quickly made to prevent significant delays in bridge construction as field problems arise. The impact and detailing requirements of tall haunches, however, are not well understood. This paper reports on 14 full-scale push-out tests conducted to evaluate the strength and failure modes of the connection between PSC girders and concrete deck slabs with varying haunch depths. Experimental results demonstrate a reduction in the peak load-carrying capacity for taller haunch specimens. With increasing haunch depth, shear failures were the primary mode of failure in the haunch region. Important factors impacting the resistance include haunch depth, reinforcing details, and concrete properties. Although the results demonstrated a reduction in strength with taller haunches, details were developed in the experiments to limit the strength reduction and provide interface shear resistance exceeding predictions from established guidelines.